Changes to Create an index

deleted the header request parameter x-api-key

the endpoint scheme security x-api-key was added to the API

api operation id create removed and replaced with indexes_create

request property models/items/model_name was restricted to a list of enum values

added the new marengo3.0 enum value to the request property models/items/model_name

removed the optional property docs_url from the response with the 400 status